I'll start;typically when I'm busy at a business stop I'll give em the"I don't know I didn't open it" or the occasional"It was a box full of money,now it's not" and my favorite reply to a residential,when I'm holding their Amazon package is" I give up,what?"
1) A very small pony.
2) I don't know. They told us to stop opening the boxes and playing with the toys.
The first one gets some to laugh and others to realize how dumb their question is. The second innocent response is an intentional double entendre which usually gets a big laugh with most and surprisingly about 10% of the time the ladies demonstrate their dirty minds and make a little mmm noise and smile.